Sintering of shaped cemented metal bodies



July 14, 1959 F, K'QLBL ETAL I 2,894,836

SINTERING O SHAPED CEMENTED METAL BODIES Filed Nov. 19, 1957 HIII! o AIN1/ENT Rs 41u94 A. Mesa-Aff@ wwf M Mm United Se@ Parent O" v 2,894,836d .Y smTERlNG or SHAPED CEMENTED METAL Booms Franz Kolbl and KarlMessmer, Reutte, Tirol, Austria, Vassignors to Schwarzkopf DevelopmentCorporation, New York, N.Y., a corporation of Maryland lApplicati-onNovember'19, 1957, Serial No. 697,449

. :s claims. (c1. VFls-zoo) This invention relates to the production ofshaped cemented metal, particle bodies containing ingredients which atsintering temperature, form a liquid phase.

vrIn the past, Adiliculties have been encountered in producing shaped`cemented refractory metal particle bodies having ingredients ofrelatively low melting temperature, because of the 'deformationof theshape of such bodies which occurred in the course of the iinal sinteringtreatmentto which they have to be subjected in order to give thenrthedesired physical characteristics and strength. Thus,'by way of example,in the case of a small gas turbine rotor formed of titanium carbideboundby an alloy of nickel chromium and cobalt forming more than about 30% ofthe rotor, it was found that its shape becomes deformed when it issubjected to the inal sintering treatment at the requiredhightemperature, such as 1300 C. to 1350* C. (Throughout thespecification and claims, all proportions are given by weight unlessspecically stated otherwise.)

Among -the objects of the invention is a sintering treatment forsintering cemented metal particle bodies containing ingredients whichform a liquid phase at the sintering temperature, which treatment willsuppress and eliminate the deformation of the desired shape of the bodycaused by the inalsintering treatments` as carried onin the past.Theforegoing and other objects of the invention will be best understoodfrom the following description of exempliiications thereof, referencebeing had to the accompanying drawing, the single figure of which shows,by way lof example, in a partially diagrammatic and par tiallycross-sectional view, one type of equipment for sintering a cementedrefractory metal particle body in accordance with the principles of theinvention.

- 'Ihe present invention is based on the discovery that the deformationdicnlties encountered in the iinal sintering, of ,cemented refractorymetal vparticle bodies are caused by the differences in thegravitational forces' acting onthe different parts of the body as aresult o'f partial softening of the lower melting phase thereof whenheated during theiinal sintering treatment. In accordance -with theinvention, the deformation di'iculties encountered in the nal sinteringtreatment of such cemented refractory metal bodies, areeliminated andsuppressed by rotating the body during the sintering operation so thatthe gravirational forces acting on dilferent por-tions of the cementedbodybalance each other. For best results, the cemented body should beArotated about one of its axes of inertia, which vare also the axes ofsymmetry of the body. Thus, in the case of a cemented body which issymmetric with respect to lan axisof rotation thereof, the body shouldbe rotated around such axis of rotation during the sintering treatment.In the case of bodies which have in onedirection materially smallerdimensions than in other directions, such as disc-like bodies, it isdesirable to rotate the body during thezsinteringroperation `about ahorizontally of equipment which has been found satisfactory for carry-`duid-guiding buckets 14 symmetrically arranged with,

respect to the axis of rotation 12. Such gas turbine rotors, which haveto operate in oxidizing combustion gas atmosf. pheres at eleva-tedtemperatures, are produced out of cemented refractory particle materialwhich exhibits the.

required strength and corrosion resistance at the elevated temperaturesat which it is exposed to the combustion gas atmosphere. used to producegas turbine rotors of the entire range of ysizes in which they arerequired. As an example, the

process of thev invention may be used for making gas .turbine rotors assmall as about 5 centimeters or even less in diameter, as well as largersizes such as upto 30 centimeters or even larger in diameter. r

As an example, vgood results are obtained with a gas turbine rotor madeby the process of the invention out of titanium carbide particlescemented by a binder alloy metal of high corrosion resistance but havinga lower meltingV temperature than titanium carbide.- As a more specicexample, good results are obtained with such gas turbine rotor having30% to 70% titanium carbide content, the balance binder metal of highcorrosion resistance and good binder properties. Good results areobtained with the binder metal formed of nickel, cobalt and ohrarmium ornickel and chromium. For binder meta-l of nickel, chromium and cobalt,the content of nickel may vary from 50% to 80%, of chromium from 20% to50%, of cobalt from 20% to 30%. Good results are obtained with a bindermetal containing nickel, 20% chromium and 20% cobalt. With a bindermetal consisting of nickel and chromium, good results are obtained with80% nickel and 20% chromium.

By way of example, in practice, good results have been obtained with agas :turbine rotor made with the process of the invention, out of suchcemented material having a diameter of 25 centimeters and weighing 9kilograms. Good results are also obtained with similar smaller andlarger size rotors having a correspondingly smaller or larger weight.

Asa further example, similarly good results are obtained with a turbine.rotor formed out of ZrBg or TiB2 lwith 5% to 20% of CrB2 in solidsolution therewith, constituting all its content or instead only 30% .to.70% of its content, and as balance either 50% to.80%r nickel, 20% to50%.ch1'omium and 20% to 30% cobalt, or 50% to 80% nickel and 20% to 50%chromium, such as 80% nickel and 20% chromium.

The process of the invention will now be described in I more detail inconnection with a specic example thereof.

disposed'inertiaaxis thereof corresponding to its largest 70 momentJofinertia.-V

p In thedrawingisshown by way of example, one type Thus, ,a cemented gasturbine rotorr is produced by the process of they invention as follows:

Example 1 l removing from the die, the green compact is, pre-sintered.

Patented July 14, 1959'` The process of the invention may be 3 in vacuumor in a protective latmosphere at a temperatureV between about 800 C.and 900 C. for three to four hours, depending on size, so as to yield lapre-sintered bodyyofz substantial strength but sufficient softness` topermitshaping by. conventionalitools to the desired final shape.. The.pre-sintering; temperature` is so chosen `as to` prevent.softening ofthe` shaped body while securing substantiallyV fullV shrinkage thereof,and, minimize Iany further shrinkage thereof in` the final sinteringtreatment. In. the. designing of the; dies for the green compact,allowance` is made for the shrinkage of the compact in the sintering.treatments andA for the shaping ofA the pre sinteredbody. The. machinedand finished pre-sintered rotorA body so obtained `is thereaftersubjected to the final; sintering treatment at an elevated temperaturebetween abo1it..1300 C. to 1350.o C. for l to. 11/2 hours depending onthe size.. By way of example, a gas turbine rotor ofz high desiredthermal shock resistance` was. made `by the process described above outof` a powder mixure.` containing 35% titanium carbide. and 65% bindermetal consisting of 60% nickel, 20% chromium; and 20% cobalt. Theresulting rotor bodies had a.A transverse `rupture strength. of 180 to200 ktg./mm.2 andv a1 specific weight of 6.9 g./cm.3.

i Therewillnow be described in connection with the drawing, how a gasturbine rotor of the type described above, was subjected to vthe nalsintcringoperation at a temperature of about 1300 C. to 1350 C. forabout one hour or more, without causing it to be deformed, in accordancewith the principles of the invention. The desired? shaped cementedbodies, such as turbine` rotors are subjected to the final sinteringoperation Within theinterior` of a furnace which, in the form shown,comprises a double-wall casing enclosure 21 formed of two spacedA walls22, 23 of heat-resistant material, such. as heat-resistant metal,confining a cooling space through whichr a. cooling liquid, such -aswater, is circulatedfor cooling the furnace-walls. The furnace enclosure21 is shown provided with a detachable double-wall section 24, likewiseformed of two spaced walls 22-1, 23-1 confining 4a cooling space throughWhich cooling liquid is. similarly circulated. The detachable enclosurewall section24 isrjoined to the main enclosure 21 along the interttingjunction Walls 25, 26, arranged so `as -to permit joining them with ahermetic seal which permits maintenance with the interior enclosurespace of the furnace either a vacuum or. a` desired protectiveatmosphere, such as hydrogen, during the sintering treatment. The turbine rotor. 10.is shown held on a rotor shaft 31 arranged to berotated,` on bearings 32. The rotor shaft is formed of refractorymaterial. The left side of the rotor shaft 31A is shown arranged to bejoined by detachable coupling connector 33 to a drive shaft 34 which isrotatably driven by a suitable drive mechanism onthe interior of thefurnace enclosure 21. The rotor shaft 31` shown is` connected by` asimilar coupling connector 33 to a similar rotor shaft of the adjacentlof a series of rightwardly disposed additional turbine rotors which areto be sintered within the furnace enclosure 21 in accordance with.theprinciples of the invention. It is to be understood-that the partof thespecification below, which dea ls with-.the 'turbine rotor 10 mountedadjacent to the left side wall of the furnace enclosure 21, apply alsoto each of the other similar turbine rotors which are subjectedsimultaneously to a similar final sintering operation within thefurnaceenclosure 21.

The drive shaftV 34 by which the rotor shaft 31 of the turbine rotorl isdriven, `is shown seated for rotation in aabearing 35l mounted in theleft side wall of the furnace enclosure 21. The bearing 3S is of a typewell known inthe artrthat provides hermetic seal between the interiorfandthe exterior of thefurnace enclosure 21' while permitting the shaft34 passing therethrough to rotate therein `for driving through couplingconnector 33, the rotorsha-ft: 31 together with the turbine rotor `10lheld CII thereon, andother similar turbine rotors which are beingsintered within the furnace enclosure 21.

The region of each of the turbine rotors 10 positioned within thefurnace enclosure 21 is sho'wn arranged to be heated by `an array ofheater bodies shown in the form of heater rods 41 of a materialssuch asmolybdenum or molybdenum disilicide, which are arranged so as to` besupplied with electric heating current as through electric connectorbars 44 extending from Water cooled electric connector terminals 45`insulatingly mounted and( passing through the wall portions ofthefurnaceenclosure 21. In order to` protect the interior Wall surfacesV of? thefurnace enclosure 21 against` the heat radiated by` the heater bodies41, a plurality of heater screens, shown L by dash lines 46 andiformedofsheets of refractory metal,

such as molybdenum, are interposed between the heater bodies 41 and theinterior wall surfaces of the furnace enclosure 21. Inlorder tolmaintain the sintered body 10 at adesired uniform` andbalancedtreatmentftemperature, there is` provided within `the furnace enclosure212', a further.` inner heat-balancingrenclosure: 51 enclosing andsurrounding thelspace occupied by the rotor10.`

The. innen enclosure 511 may beiformedrof refractorymetal such4 asmolybdenum sheetv material andmay have a detachable. wall section 52 on`the upper `sidef'offthe adjacentnregionof the detachable walla24 of' thefurnace enclosure `21. In the Aform` shown, the bearings 212 on whichvthe rotor shaft 31'- is suit-ablyA mounted Iwithin the walls of theinner enclosure 51 surrounding the cemented rotor 10IwhichV is to1 be=sintered, may be-formed` off re'- fractory ceramic material ofthe' typeusedy in'- similar applications, `which will retain its strength at thehighA temperatures at' 'whichA the interior of the furnace is' heated;'Ihegeneral details of` thel structural features 0f' the sinteringfurnace of the type shown, except#` for the arrangement whereby thesinteredbody is tohbe rotated therein, are of- Wellrknown constructiongenerally used inthe pasti for finally sintering cemented refractorymetal particle bodiesv andA need not be described inY more detail. Therotol'fshaft 31 onwhich the cemented rotor 10= is. seated, the driveshaft 34- and the shaft' connector 33 are made of a solidmaterialV thatwillretain! its strengthrat the elevated@ furnaceytemperature, such astungsten` or molybdenum.

Therinteriorof the sintering `furnace 2,1l vis-'heated by heatingcurrent suppliedl tothe heater bodies;41\ for bring ing andV maintainingtherotor 10 at the desired sintering temperature in the range betweenaboutI 1300* C. to 1350io C. The interior space withinthe furnaceenclosure 21 is evacuatedr by a suitable vacuum connection,not'shown,.so as toi maintain thereinay vacuum of about 0.1A to OLOS mm.of a mercury column. Throughout the time the interior of the furnaceenclosure Z1 is heated. to a` raised temperature at which the bindermetal of the rotor might develop a liquid phase or mightsoften, therotor 10is rotated by applying arotary` drivingforcerto theouter end` ofthe drive shaft 34. The rotor10 isy kept rotating for the entireVperiodlof 1 to2 hours required for completing the final sinteringtreatment wherein its body is given the desired` physicalcharacteristics. After performing the sintering ytreatment-the heatinglis stopped and the interior of the` furnace is cooled, the rotorV` 10beingrkept rotating untilitstemperature has been broughtdownconsiderably below the temperature at which the binding`metal'thereof hasany liquid*l phase or a-tendency tosoften, such asatemperature'of 8009 C.V orlower.

Inlmaking gasturbine rotors by a process of therinvem tionof thetyperdescribed above, it has been found advantageous to incorporatesmalliamounts of molybdenum inthe mixture of the. powder` ingredients`outof which the gas turbine rotor is formed. The addition ofa smallamount of molybdenum. eliminates free: carbon and p oxygen which' ifpresent would` detract' from the `physical ture of`600 C. to 900 C. fora pre-sintering time of about .l'hour and up Ito 3 or 4 hours, dependingon the siz'e. The machined and finished pre-sintered rotor body issubjected to a final sintering temperature of 1200 C. to l400 C. for lto lll/z hours.

Very good results have been obtained with the process of the inventioncarried on within the range of conditions outlined above, with a gasturbine rotor having an outside diameter of 8 inches and larger.

In the sintering operations, during which the gas turbine rotor issubjected to elevated temperatures at which its binder may becomesoftened, the gas turbine rotor is rotated around an axis of symmetrythereof to prevent ow of the softened or liqueed binder metal due to thegravitational forces acting thereon. In practice, slow rotation f thegas turbine rotor such as at l r.p.m. (revolutions per minute) or asomewhat slower or higher rate,

s uch as rpm., is sufficient to prevent gravitational ow or creep of theheated softened binder metal.A By such slow rotation, the direction ofthe gravitational 'forces acting on the softened binder metal iscontinuously changed atla rate at which they are insulicient to causeany movement or displacement of the softened binder metal of therotonwhile it is heated during the sintering operations. By' rotatingthe rotor in the manner described above to prevent flow or creep ofbinder met-al While the rotor is subjected to the elevated ntemperatureof the sintering furnace, runiform and homogeneous distribution of thebinder metal is assured, and the danger of nonhomogeneity avoided, acritical factor for rotors whichV is"formed. Thus, in the case of-a gasturbine rotor of 35% TiC cemented by 65 %l of the binder metal, asdescribed above, having an outside diameter of 20 centimeters,go'odresults are obtained by rotating the rotor at a'rat'e of about 4 to5 r.p.m. while it is maintained at the elevated sintering temperaturejOn the other hand, in the case of a similar gas turbine rotor of thesame material' having an outside diameter of about 14 centimeters, goodresults are obtained by rotating it at a rate of 2 to 3'r.p.m. 'Rotorsmade with a smaller content' of the binder metal, may be rotated lat asmaller speed to prevent gravitationalffow or creep of the binder metalwhich is somewhat softened at the elevated sintering temperature. `Ingeneral, a relatively low speed of rotation, of at most 200 revolutionsper minute, will be suicient for preventing deformation of .a cementedbody as a result of softening of fa liquid phase thereof during thesintering operation.

The sintering method of the invention is. not limited to forming shapedcemented bodies of the type described above, but is of great valuegenerally in the production of'all types of sintered cemented metalparticle bodies containing ingredients which form a liquid phase at thevhigh sintering temperature to which they are subjected, because theaction of the gravitational forces on the liquid phase of such bodyduring the sintering may cause displacement of portions of the liquidphase, thereby disturbing the homogeneous character of the sinteredbody, a factor which is of great practical importance in manyapplications of sintered cemented refractory bodies. Thus, -forinstance, lack of homogeneity in a rotary body will develop largeunbalancing forces during high-speed rotation of such body and willrequire careful balance test vtoi ydetermine the radius of unbalance,followed b y.

careful removal of accurately determined. portions ofthe body for givingthe body the -desired dynamic balanceQv Lack of homogeneity in the partsof a cemented body may lalso cause critical distortions thereof whensubjected to heat shocks.

Among the applications in .which the sinteringftreatment of theinvention is of great value, is the productiony of cemented particletool elements, Y cemented-particle guides or nozzles for guiding ordischarging liquid metal, cemented-particle sockets, and various othershaped cemented bodies. Additional examples of sintering treatments ofthe invention will be described below.

Example 2 A spiral heating element is made out of a powder mixturecontaining MoSiz particles and 10% CrB2, ground to a particle size of-50 microns.' The powder mixture having admixed thereto a plasticizingaddition such as 2% of parane and having a dough-like consistency, isextruded in an extrusion press into an elongated strand. While stillplastic, the strand is wound. on a. suitable cylindrical support into aspiral heater body having turns of circular shape, and dried on thesupport. After drying, the spiral is positioned on a sufpport ofsmaller' diameter than'its turns with theend portion of the spiralsymmetrically held relatively vto the central support by end members ofrefractory material such'a's porcelain, seated on the'support andengaging the end turn of the spiral.

jected to a sintering treatment at about 1800 C. in* a hydrogenatmosphere for 15 minutes, while the spiral heater and its support arerotated at a rate of 5 revolutions per minute. Such spiral heater, whensintered without rotation while suspended vertically, would causean-enlargement ofthe lower spiral turns. Such spiral heater whensinteredwithout rotation while in a hori-A zontal position, would cause thecircular spiral turns to be deformed into oval shape.

Example 3' ings, andkfor molds used for casting reactive metals,jfor

protecting thermocouples placed in liquid bodies such as moltenaluminum, and in like applications. shaped article is sintered while itis Abeing rotated vat the rate ofl about 5 to -10 turns per minute in asintering furnace. To permit rotation of the shaped article beingsintered, it is formed with end portions along which-itmay be rotativelysupported in suitablebearing supports within the sintering furnace.After completion of the, sintering treatment, the end portions areground away, leaving the desired shaped body. Such shaped articles, whenmade without rotary sintering supports of the invention, .would undergodeformation under the action of gravitational forces while it issoftened by carbide, 5% of tantalum carbide, 8.5% cobalt, and thebalance tungsten carbide, is compacted into a thin cylinder,

the thickness of which is such that after shrinkage, it will have thethickness of the desired spiral tool elements which are to be secured onthe cylindrical support sur- The support with the spiral are thensintered in a sintering furnace and sub-V 7 faceofthe` steelv rotor;After an initial presintering at about1800 C. to: 1000. C. for to' 10minutes, the pre siriteredr` compact is subjected to a groovingoperation for forming out of the cylindrical' sintered compact al fplurality of spirally-shaped elements joined and supported at theVopposite ends by a continuous end ring collar. After' placing theso-obtained generally cylindrlcal body f on' a cylindrical graphite rodon which its end collars i Example 5 l For shield'containers forradioactive substances formed oftungsten bound with 5% nickel and 2%copper, it isy essentialtto secure absolutely uniform distribution andhomogeneity ofthe ybinder metalV content throughout the body of thecontainer. A cyli'ndrically` shaped'radiation shield is prepared' by`subjecting the compact formed of a lrnixtureofl several powderingredients to sintering for 10Hto l5 minutes at l"400 C. to l450 C.undery hydrogen while the shield body is being rotated aty a ratev ofklive turnsl per minute; kDuring the sintering operation, the' body issupported on a cylindrical ceramic support which forms the rotatingsupport thereof. the great difference between the specific weight oftungA sten' and its copper-nickel content, the gravitational forcesacting thereon duringsintering, while itY contains a liquid phase, willlcause non-uniform distribution of its nickel'- copper content, if it is`not rotated duringA the sintering treatment' in accordance with' theinvention.

Exampie 6 Air-foil shaped turbine` buckets. or vanes are formed out oftitanium carbide cemented with 50% of a nickelchromium-cobalt alloy. Thepowder compact formed of the titanium carbide and the alloy, is providedat its opposite ends with rotaryA support `projections which are groundofftherefrom after completing the sintering. The rotary end portions ofthe compact are 4arranged coaxial with its `inertia axis. Afterpreliminary sintering of the compact at about 800 C.-l000 C., it issubjected to anadditional shaping operation. Thereupon it is subjectedtoA additional sintering while it is being rotated on its endprojections under vacuumV for 10 minutes at a sintering4 temperature of`1250l300 C., at which a liquid phase is formed of some of its contents.Although suchl bucket is only 7` inches long, such sintering treatmentwillcause slight deformation thereof as a result of the gravitationalforces acting thereon while it is softened? by the liquid phase formedtherein during the sliort-` sintering treatment. The removal of thedefects causedby the deformation involves expensive, careful machining,which is eliminated by rotation thereof during the sintering, inaccordance with the invention.

Instead of providing a direct mechanical coupling conneetion between theexterior drive shaft and the rotor shaft 31, the mechanical drivingconnection may be provided in some other way, for instance by a magneticclutch between a magnetic member of the external drive shaft and amagnetic member in the interior of the furnace enclosure 21 which has amechanical connection to the rotor shaft 31.

Because of- This application is a continuation-impart of our coe:pending `application* Serial'No. 3813598', tiled September 2,2, 1953,now abandoned.`

The features and principles underlying the invention described above in`connection with specific expernplic :`2 1`` tions, will suggest to`those skilled' in the art manyother modifications thereof. It isaccordingly desired that the appended ,claims be construed` broadly andthat 'they shallnot belimited to thel specific details shown .and defscribed in connection with exemplitications` thereof.

We claim: v 1. The method of sintering a homogeneous cemented bodyconsistingof cemented refractory particles selected from the groupconsisting of the refractory metals, the

carbides, the borides and the silicides` of refractory. me.-

tals and mixtures thereof, which body contains ingredientsV which form aliquid phase att-he sinteringternperature, the procedure comprisingrotatably supporting said body along an axis, subjecting said body whileso supported to sintering' for at least lO minutes at a sinteringAtemperature of at least about 1100? C. at' which a liquid phase isformed of some of its ingredients tending to soften saidbody, and slowlyrotating` said body about' said axis while it is being sintered at saidsintering temf perature in such manner that the direction of, thegravitational forces acting on said liquid phase and other portions ofsaid body is continuously changed at arate at.`

which said gravitational forces are insuliicient to cause any movementof portions of the liquid phase and'` of any other portions of said bodyrelatively to` each' other be# cause ofsofteningof said liquid phasewhile being subjected to said sintering treatmen.

2,; The method of sintering a cemented body as claimed inclaim 1,wherein said body is rotated about an axis yhaving the greatest momentof inerti-a.

3. The method of sintering a homogeneousk cemented` f body which issymmetric with respect to a central axis` and consists of cementedrefractory particles` selected from the group consisting of therefractory metals, the.

carbides, the borides and the silicidesof refractory metals and'mixtures thereof, which body contains ingredients which form a liquidphase at the sintering temperature, the procedure comprising rotatablysupporting saidbody along 4said axis, subjecting said. body while sosupported.

to sintering for at least l0 minutes at a sintering temperature of atleast about 1100 C. atrwhich a liquid phase is formed of some of itsingredients tending to` soften said body, and slowly rotating said bodyabout said central axiswhile it is being sintered at `said sinter ingtemperature in such manner that, the direction ofthe gravitationalforces acting on said liquid phase` and other portions of said body iscontinuously changed at a rate: at which said gravitational forces areinsuicient to cause any movement of any portions of the liquid phase andof any other portions of said body relatively `to each other because ofsoftening of said liquid phase. while being subjected to said sinteringtreatment.

4. The Vmethod of sintering a cemented body as claimed in claim 1,wherein` said body is rotated until" the temperature of said body islowered from the elevated temperature of sintering to a level at whichall binder metal content ofV said body is solidified.

5. The method of sintering a cemented body as claimed in claim 3,wherein said body is rotated -until the telnperature of said body islowered fromthe elevated tem-` perature of sintering to a level at whichall binder metall content of said body is solidified.

No references cited.

' MBL 3L,

UNITED STATES PATENT OFFICE ,f CAT 0F 0N Patent N00 2,891,836 v July 14,1959 Frenz Kolbl et al.,

It is hereby certified that error veppeers in the above numbered patentrequiring connection ,and that tne lseid Lettere Patent should read .ascon@ nested belowo In thev heading to tbev printed specification,between lines "7 and 8, insert =m Claims priority,. application AustriaGctobe' 1, 1952 (SEAL) Attest:

ROBERT C. WATSON Attesting Officer comissioner of Patents UNITEOsTATEsPATENT OFFICE CERTIFICATE 0F CORRECTION N00 ,891,836 y l July 14, 1959Fra-nz Koibi et an t iS hereby certified that error ,appeans in theabove numbered patent requiring correction and. that the ,said LettesPatent should read .as con rested belowo In the heading tol ther printedspecification, between lines '7 and 8,

' insert m Claims priorityy application Austfia October l, 1952 Signedand sealed this 8th day of December 1959.,

(SEAL) KARL -10 Attest:

, ROBERT c. WATSON Atiiesli'ldlgl Officer Conmissioner of Patents

1.THE MOTHOD OF SINTERING A HOMOGENEOUS CEMENTED BODY CONSISTING OFCEMENTED REFRACTORY PARTICLES SELECTED FROM THE GROUP CONSISTING OF THEREFRACTOR METALS, THE CARBIDES, THE BORIDES AND THE SILICIDES OFREFRACTORY METALS AND MIXTURES THEREOF, WHICH BODY CONTAINS INGREDIENTSWHICH FORM A LIQUID PHASE AT THE SINTERING TEMPERATURE, THE PROCEDURECOMPRISING ROTATABLY SUPPORTING SAID BODY ALONG AN AXIS, SUBJECTING SAIDBODY WHILE SO SUPPORTED TO SINTERING FOR AT LEAST 10 MINUTES AT ASINTERING TEMPERATURE OF AT LEAST ABOUT 1100* C. AT WHICH A LIQUID PHASEIS FORMED OF SOME OF ITS INGREDIENTS TENDING TO SOFTEN SAID BODY, ANDSLOWLY ROTATING SAID BODY ABOUT SAID AXIS WHILE IT IS BEING SINTERED ATSAID SINTERING TEMPERATURE IN SUCH MANNER THAT THE DIRECTION OF THEGRAVITATIONAL FORCES ACTING ON SAID LIQUID PHASE AND OTHER PORTIONS OFSAID BODY IS CONTINUOUSLY CHANGED AT A RATE AT WHICH SAID GRAVITATIONALFORCES ARE INSUFFICIENT TO CAUSE ANY MOVEMENT OF PORTIONS OF THE LIQUIDPHASE AND OF ANY OTHER PORTIONS OF SAID BODY RELATIVELY TO EACH OTHERBECAUSE OF SOFTENING OF SAID LIQUID PHASE WHILE BEING SUBJECTED TO SAIDSINTERING TREATMENT.